(a) Field of the Invention
The invention relates to an exhaust gas purification catalyst and an oxygen storage component for the same.
(b) Description of the Related Art
Exhaust gas purification catalysts, such as three-way catalysts, for removing hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxides (NOx) in exhaust gas from an engine contain catalytic precious metal, such as platinum (Pt), palladium (Pd) and/or rhodium (Rh), supported on a support material. If the amount of supported precious metal is increased, the capacity to remove the above pollutants in exhaust gas can be enhanced theoretically. Actually, however, the capacity is deteriorated because of sintering of precious metal due to exhaust gas heat. In addition, the increase in the amount of precious metal leads to cost rise. Therefore, a significant challenge in developing catalysts is to place catalytic precious metal in a highly dispersed manner on and in a support material.
Japanese Unexamined Patent Publication No. 2004-174490 discloses, as a technique for highly dispersing catalytic precious metal on and in a support material, that on wall surfaces of each cell of a honeycomb support is formed a catalytic layer which contains active alumina and an oxygen storage component made of a mixed oxide containing cerium (Ce), zirconium (Zr) and neodymium (Nd) and doped with rhodium (Rh) serving as a catalytic precious metal to place its atoms at and/or between crystal lattice points of the mixed oxide, that the mass ratio of ZrO2:CeO2:Nd2O3 is 72.8:24.5:2.6, and that the amount of Rh is 0.486 mass %. In other words, the above technique aims at making Rh less susceptible to sintering while highly dispersing it on and in a support material by placing Rh atoms at and/or between crystal lattice points of the mixed oxide. Further, the above technique also aims at improving the oxygen storage capacity of the mixed oxide by virtue of Rh existing inside the mixed oxide.
Furthermore, the above publication discloses that, for Ce—Zr mixed oxides containing no neodymium, the preferable ratio of ZrO2/(CeO2+ZrO2) is 20 to 30 mass % both inclusive or 65 to 90 mass % both inclusive.